HMRC Letter: What to Do (Step-by-Step for Business Owners)

An HMRC letter can feel like a red flag, even when it is routine.

I’ve dealt with enough of these over the years to tell you this: most letters are not accusing you of wrongdoing. They are usually HMRC trying to close a gap in their information, confirm a figure, or correct something on their system.

What matters is how you respond. A clear, timely reply often ends the matter quickly. A rushed, vague reply can drag it out.

1) First: identify what type of HMRC letter you’ve received

Before you draft a response, work out what you are looking at. HMRC uses different processes, and the right approach depends on which one applies.

1.1 Compliance check vs enquiry vs assessment

• HMRC compliance letter: HMRC is checking something specific, often one return, one figure, or one area (VAT, PAYE, Corporation Tax, Self Assessment).
• HMRC enquiry: a formal enquiry into a tax return. This can be more detailed and can involve multiple questions over time.
• Assessment or determination: HMRC has raised a tax figure, sometimes because information was missing, late, or they believe a return is incorrect.
• Penalty notice: usually linked to late filing, late payment, inaccuracies, or VAT-related penalties.

1.2 The deadlines and reference numbers to look for

In the first minute of reading the letter, find:

• The response deadline: the date they want your reply by, not just the letter date.
• The reference number: often essential for routing your reply correctly.
• The tax type and period: for example VAT quarter ending, payroll month, accounting period, or tax year.

If those three things are unclear, you are already at risk of sending the right answer to the wrong question.

2) Common reasons HMRC sends letters to businesses

Most letters fall into a handful of patterns. Knowing the pattern helps you gather the right evidence fast.

2.1 Something doesn’t match HMRC’s data

HMRC compares information from different sources, such as:

• VAT returns vs accounts and Corporation Tax computations.
• Payroll submissions (RTI) vs reported expenses or benefits.
• Interest, dividends, or other third-party reporting vs Self Assessment.

If a number looks “off”, HMRC often writes asking you to explain the difference.

2.2 A VAT return triggers questions

VAT is a common trigger because patterns stand out quickly. Typical triggers include:

• Unusually large input VAT reclaims.
• Repeated VAT repayments.
• VAT on atypical purchases, like vehicles or mixed-use items.

2.3 Late filings or late payments

Sometimes the letter is administrative rather than investigative, for example:

• A reminder that a return is outstanding.
• A notice of late filing penalties.
• A nudge about a payment plan or arrears.

2.4 Random checks and sector campaigns

HMRC does run targeted activity in certain sectors and also selects some cases for routine checks. That can look personal, but it often is not.

2.5 PAYE, payroll, and CIS queries

If you run payroll or CIS, letters can be triggered by:

• PAYE payments not matching submissions.
• Late RTI filings for one or more pay periods.
• CIS verification, deductions, or missing subcontractor details.

3) HMRC letter what to do: the 10-step response plan

If you want a simple process you can follow every time, use this. It keeps you organised and reduces the chance of an accidental misstatement.

3.1 Read, file, and don’t phone in a rush

Read the letter twice. Save a scanned copy. Start a folder for:

• The HMRC letter and envelope scan.
• Your draft response and final response.
• Supporting evidence and reconciliations.

If you call immediately, you are likely to answer before you have checked your figures. That rarely helps.

3.2 Check the deadline and how HMRC wants a reply

Some letters ask for a written reply, others allow online messaging, and some provide a phone number. Match the channel they request, unless you have a good reason not to.

3.3 Confirm the letter is genuine

It is sensible to be cautious. Check:

• The letter matches the tax account you actually have (VAT, PAYE, Corporation Tax).
• Reference numbers look consistent with prior HMRC correspondence.
• You do not click links or open unexpected attachments.

If you are unsure, use official GOV.UK contact routes rather than numbers in an email, and never share passwords or full bank details.

3.4 Work out exactly what HMRC is asking

Highlight the specific questions. HMRC letters often contain:

• A request for an explanation of a figure.
• A request for documents, like invoices or bank statements.
• A request for a breakdown, like sales by month or expenses by category.

If the question is vague, your reply should be structured enough to remove ambiguity.

3.5 Gather evidence and reconcile the numbers

Do the reconciliation before you respond. Examples:

• VAT return boxes reconciled to the VAT control account and sales/purchases ledgers.
• Turnover on accounts reconciled to bankings and invoicing reports.
• Payroll totals reconciled to RTI submissions and PAYE payments.

If you find an error, deal with it head-on. A small correction early is usually easier than an argument later.

3.6 Draft a clear, plain-English response

Your aim is to help the HMRC officer close their question. I normally use this structure:

• Restate their question in one line.
• Give the answer in one or two lines.
• Explain the reconciliation, with numbers.
• Attach labelled evidence that supports the reconciliation.

Keep it factual. Avoid emotional language, speculation, or long backstories.

3.7 Only send what’s requested (and keep copies)

Send enough to answer the question, but don’t flood them. If you send 200 pages, you increase the chance they find something else to query.

Keep a copy of everything you send, including:

• PDF of your letter or message.
• List of attachments with filenames.
• Date and method of submission.

3.8 If you need more time, ask properly

If the deadline is tight and you are gathering records, ask for an extension before the deadline. Be specific:

• Say what you are collecting.
• Say when you can respond.
• Confirm you will send an interim update if needed.

3.9 If you disagree, challenge the right way

If HMRC has assessed tax or issued a penalty you believe is wrong, there are formal routes like an appeal or review. Your response should:

• State what you disagree with and why.
• Reference the tax period and the notice date.
• Include evidence, not just opinion.

If you are unsure which route applies, get advice before you send anything. One poorly worded sentence can create an unnecessary admission.

3.10 Track the outcome and update your records

Once you have replied, diarise follow-up dates. When HMRC responds, update your internal records so the same issue does not repeat.

4) How to respond to specific HMRC letters (quick playbook)

Below are the most common letter types I see for owner-managed businesses, and what tends to work best.

4.1 HMRC compliance letter: what they usually want

A typical HMRC compliance letter asks for one of three things:

• A clarification of a figure, such as turnover or expenses.
• Evidence for a claim, such as input VAT or a deduction.
• A breakdown of transactions, such as sales by customer or purchases by supplier.

Your response should include a short reconciliation and clean attachments. Name your files clearly, for example “VAT_QE_31Mar2026_InputVAT_Reconciliation.pdf”.

4.2 HMRC enquiry: what happens next

An HMRC enquiry is more formal. Expect a process rather than a one-off letter.

Common steps include:

• HMRC confirms the scope of the enquiry and what they will review.
• You provide documents, explanations, and reconciliations.
• HMRC may ask follow-up questions, sometimes in rounds.

If you have an enquiry letter, it is usually worth involving your accountant early. It keeps the communication tidy and reduces the risk of mixed messages.

4.3 VAT assessment or VAT penalty notice

If HMRC issues an assessment or penalty, check:

• Which return or period it relates to.
• The basis of the penalty, such as late filing or inaccuracy.
• Whether there is an appeal window and what evidence is needed.

If the penalty is due to a genuine one-off issue, you may have grounds to appeal, but you need to do it within the time limit and with a coherent explanation.

4.4 Corporation Tax or Self Assessment queries

These letters often relate to:

• Director’s loan account movements and repayments.
• Large expense categories, such as travel or motor costs.
• Differences between accounts and returns.

Good answers here are numbers-led. Tie your explanation back to your bookkeeping, accounts, and supporting documents.

4.5 PAYE coding, RTI, and payroll issues

Payroll letters can be frustrating because they may be driven by timing or allocations. The key is to match:

• RTI submissions to the payroll reports for the same dates.
• PAYE payments to HMRC’s allocation across months.
• Any adjustments, like statutory payments or EPS filings.

If something is misallocated, a structured schedule showing dates, amounts, and references can resolve it quickly.

5) What not to do when HMRC writes to you

There are three mistakes I see that turn a simple letter into a long-running issue.

5.1 Don’t ignore it

Ignoring HMRC is the fastest route to escalations, penalties, or estimated assessments. Even if you cannot answer fully, acknowledge and request time.

5.2 Don’t guess numbers to ‘make it go away’

Guessing can create an inaccuracy problem where none existed. If you need to investigate, say so, then come back with reconciled figures.

5.3 Don’t send a box of paperwork with no explanation

Evidence without context is slow to review and can prompt extra questions. Give HMRC a simple roadmap: what each attachment is, and how it supports your answer.

6) When to bring in an accountant (and why it often saves money)

Some HMRC letters are straightforward. Others have more at stake than they first appear.

6.1 Signs the letter is higher risk

• It is a formal HMRC enquiry notice.
• It involves large figures, repayments, or multiple tax periods.
• HMRC is asking about personal use, benefits, or director-related transactions.
• You suspect your bookkeeping is not up to date.
• You are unsure whether you have made an error.

6.2 What we do at AVMK Accountants

At AVMK Accountants, we focus on being proactive and clear. If you receive an HMRC compliance letter or enquiry, we can:

• Review the letter, identify the real question, and assess the risk.
• Reconcile the numbers back to your bookkeeping, VAT, payroll, and accounts.
• Draft a plain-English response with the right evidence, presented cleanly.

For many business owners, the bigger win is what happens after the letter: we tighten the process so the same trigger does not come back next quarter.

6.3 What you can prepare before the first call

If you want the quickest route to clarity, gather:

• A scan of the full HMRC letter, including any enclosures.
• The tax period involved and the return submitted.
• Supporting reports, like VAT detail, nominal ledger, payroll summaries, and bank statements.

If you do not have these to hand, that is not a problem. It just tells us where to start.

7) FAQs: HMRC letters for business owners

7.1 How long do I have to reply to an HMRC letter?

It depends on the letter type. Many HMRC compliance letters set a deadline, commonly around 30 days, but it can be shorter. Use the deadline written in the letter and act early if you need an extension.

7.2 Can HMRC fine me if I reply late?

Late responses can lead to escalations, and in some cases penalties, especially where HMRC has requested information formally. If you cannot respond in time, ask for more time before the deadline and keep a record of that request.

7.3 Will an HMRC compliance check turn into an enquiry?

Sometimes a narrow check becomes wider if HMRC finds inconsistencies or cannot reconcile what you send. That is why a structured, numbers-led response matters. It helps them close the point quickly.

7.4 Should I call HMRC or write?

If the letter asks for a written response, write. Phone calls can be useful for clarifying what they want, but I prefer to confirm anything important in writing afterwards, so there is a clear trail.

If you’ve received an HMRC letter and you want a second pair of eyes before you reply, I’m happy to help. AVMK Accountants offers fixed-fee support and plain-English advice, so you know where you stand before you send anything.

If you need help, book a free initial consultation.